Mineral oil composition resistant to foaming



Patented Mar. 26, 1946 MINERAL on. COMPOSITION nnsrs'mn'r 'ro FOAMING Herschel G. Smith, Wailingford, and Troy L. Cantrell, Lansdowne, Pat, assignors to Gulf Oil Corporation, PittsburglnPa a corporation of Pennsylvania No Drawing. Application September 21, 1942,

Serial No. 459.180

Claims.

This invention relates to improved mineral oil compositions resistant to foaming.

In lubricating machinery with oils, and in handlingoils as by pumping, conditions are often such that the oil is subjected to violent a itation in the presence of air or other gases: conditions such as to produce foam or froth. In some cases foaming or frothing is quite objectionable. For example, in lubricating automobile gearing (in the gear box, and rear axle) foaming produced by the churning of the gears gives rise to excessive leakage and loss of lubricant past retainer rings. etc.- Moreover, foaming seriously interferes with the proper functioning of the oil. Automobile gears such as those used in transmission and differentialgear assemblies often operate at very high speeds, as well as under high tooth pressures; therefore, they require a very good lubricant to prevent or retard excessive wear due to metal-to-metal contact, and foaming is undesirable. The lubricants employed are viscous oils, often containing a so-called extreme pressure agent to assist in maintaining an oil film between the teeth; sulfurized sperm 011. being especially good. If the lubricant contains air dispersed through it, it lacks proper fllm foaming properties. Moreover, foaming oil is much less effective to conduct heat away from the working zone. These difflculties are often aggravated by the fact that some extreme pressure agents present in the oil actuallyincrease the foaming characteristics of the oil composition.

- Foanfing is also objectionable in other situations; for example, during the pumping of oils, and in compounding oils with extreme pressure agents and other additives-an operation involving thorough agitation. Nearly all petroleum oils foam to-some extent under violent agitation; the more viscous the oil the greater the amount of foam and the longer it persists after agitation is stopped.

Among the objects of our invention are the provision of gear lubricants and other lubricating compositions which are characterized by freedom from tendency to foam or froth even under severe conditions.

We have discovered that foaming of petroleum oils, even under the most violent conditions de- 5 scribed, can be suppressed or prevented, by incorporating in the mineral one small proportion of a lutidine isoamyl octyl phosphate. This class of lutidine'phosphate compounds may be represented by the following generic formula:

wherein R represents a methyl group.

, These aminophosphate salts can be readily prepared from the commercial lutidines, which are mixtures of the dimethyl pyridines. Likewise, substantially pure lutidine compounds, such as 2.,6-dimethyl pyridine, etc., may be employed in making our improvement agents. The salts obtained from 2,6-lutidine are advantageous for the present purposes. I

. In general, dissolving almost any additive agent in oil has a tendency to increase foaming more or less. The above lutidine salts are remarkable in that theysuppress foaming, even when present in small amounts. They have no deleterious efiect .on the lubricant properties or other properties of the oil.

-These agents can be incorporated in all sorts of oils, to achieve the stated results. One particularly advantageous field of use is in gear lubricants for automobiles and the like. As stated,

40' these lubricants are viscous and they contain extreme pressure agents or other additives; both of which facts make for heavy foaming. By dissolving a fraction of a per cent of our new agents, foaming is prevented. For example, such a gear lubricant, within the purview of our invention,

liquid has the following composition (-per cent. by

' provement agent or aminophosphate may be repweight) v Refined high-viscosity lubricating oil 89 to 95 Refined sulfurized sperm oil 5 to 2,6-lutidine isoamyl octyl phosphate- 0. 01 to 1. 0

- foaming,

Inpreparing the new agent, lutidine is brought into reaction with isoamyl octyl acid orthophosphate, and the pH of the reaction mixtureis adjusted to within the range 2.0 to 5.5. With the theoretical molecularratio of the two'reactants,

namely 1:1, the product is apt to be slightly too acid, with a pH below 2, and this is taken care of by using a slight excess of the lutidine, so

that the molecular ratio is between 1:1 and 1:1.1.

The reaction product is an oily liquid. dissolves in oils or oil compositions.

The proportion of the agent to be dissolved It readily in the oil or oil base depends on the viscosity of the 011, its ingredients, and the severity of'the conditions of use. Ordinarily, 0.01 to 1.0 per cent of the agent by weight of the oil is employed; the lutidine isoamyl octyl phosphates being very effective agents for the present purposes. I

Isoamyl octyl orthophosphate is a brown, oily and its viscosity 210, 75, and 29 centipoises at 25, 50, and 75 C. respectively. It is insoluble in water and soluble in mineral oils to the extent Its specific gravity is 1.009 at 24/4 C. y

of 11.70 parts in 100 parts of oil at 20 C. The

orthophosphate decomposes at 302 to 311 F. It has the structural formula:

As stated ante, the above acid phosphate ester readily reacts with the lutidine to form amino- .phosphatejsalts, which ar advantageous for the present purposes. In making such salts, commercial lutidines ma be employed. However,

we usually employ 2,6-lutidine, as the phosphate salts thereof are advantageous foam suppressors. This particular lutidine compound is also known as a,a'-lutidine, or 2,6-dimethyl pyridine. It is a mobile liquid, having a specific gravity of 0.942 at 0 C. It boils at 142-3 C., and has a molecular weight of 107.15; its formula being as follows:

The 2,6-lutidin is soluble in water and in various organic lvents, such as alcohol, ether, benzine, benzol and fatty oils.

The aminophosphate esters prepared from 2,6-- lutidine are likewise readily soluble in. hydrocarbons, particularly petroleum oils. This imresented by the following formula:

As statedante, and further shown post, the above aminophosphate is an excellent improvement agent in mineral oil compositions, and very effectively suppresses the foaming of such oils and oil compositions. I

; The following example illustrates one advantageous way of preparing our foam suppressor:

Example I .One hundred and seven pounds of 2,6-lutidine were added to an iron vessel equipped with an air' lance, and 281 pounds of 'isoamyl octyl orthophosphate were introduced over a period of one hour; the slow rate of addition being desirable to maintain the temperature of the reaction mixture below 212 F. At-the conclusion ;of thisreaction, the temperature was 180 F. and the pH of the mixture was 2. A pH "of 3.5 was desired; 11 pounds of lutidine were added, which brought the pH'to 3.5. The reaction product was an oily liquid. It was readily soluble in mineral oils. Lutidine salts of is'oamyl octyl phosphate are new chemical compounds which are claimed in our copending application, Serial No. 640,666, filed on January 11, 1946, as a'continuation-in-partof the present application.

As the 2,6-lutidine isoamyl'octyl phosphate is substantially insoluble in water, the pH equivalent is measured. by the following expedient. Normal butanol (which contains a small amount of water) is adjusted to exact neutrality, pH='7.0, and the sample is dissolved therein. I 'he pH of the solution is then measured in the ordinary way as for aqueous solutions, by electrometric or colimetric" methods. The butanol appears to serve as a blending agent for dissolving the sample in water, so to speak.

It will be noted that the measured pH of the aminophosphate is low despite the fact that a slight excess of amine is present. This is because the reaction involves neutralizing a rather strong acid with a very weak base.

Moreover, traces of 'mono-, di-', and tribasic acids may be formed under the conditions of the pH determination. At any rate. the results are as stated. a

The following example illustrates the preparation of a gear lubricant in accordance with the invention.

Example II.A highly viscous, highly refined Pennsylvania oil was selected as the base, and in it was dissolved 0.04 per cent of the oily reaction product of Example I. As shown in the following table, the change in viscosity and in color by incorporation of the agent was negligible.

Composition Straight oil Improved oil Color, NPA 4. 75 4. 75

To evaluate the foaming properties of the straight oil and the improved oil, samples (500 cc.) of the two oils were subjected to foam test No. 1 (described below). The results were as of the oil, as secured on-the compounded oil before the addition of the foam suppressing agent, were the same as the corresponding tests made follows: after the addition of the indicated amount of 5 this foam suppressor. Composition Straight oil Improved oil In other wordsythe characteristics of the two lubricants were practically the same-except for At end of stirring: the foaming properties. The following are com- Qgigjgfi't'fifl 23 parable tests (the nature of whichis described in Ratio 1 3 48 1.03 detail below) on these properties. The samples agggmgfgi. H 77 were 500 cc. each, the speed of the agitators 550 g r es of oil and foam, cc {103 RPM, and the initial temperature 77 F. NetmeIIIlIIIIIIIIIIIZI Fine Noioam Foam tests l5 Ratio MW- gg New lubricant It will be observed that the straight oil developed twice its volume of foam under the conditggg g gggi fig tions of the test and that an appreciable volume 0 011+:om ,CCLHIIIIIIIIQIIIIII 1,1361" III sob. of foam remained even after an hours standing W 3.50 1.08... 1.18. while the improved oil developed only a negligible Mm p3,; 1 inning amount of foam, which was all gone at the end ap m 0F 77 77 77 of an hour. oiiiit,$1...::::::::::::::::: 665:3: 606113;: 506. Decreasing the percentage of 0.01 still leaves 5 1m the oil much less susceptible to foaming than the 2 m-,j g Emu None Nam straight oil;

The foam suppressor as stated can be added to compounded lubricants to prevent foaming thereof. It is compatible with most of the other types of improvement agents now employed and the amount required to prevent foaming in such compounded lubricants is relatively small and does not deleteriously affect the other properties of compounded lubricants. This is an important part of the invention, as certain of the agents employed to impart particular properties to lubricating oils have been found also to promote the foaming of the oil composition when agitated. By adding even traces of the present foam suppressor, such compounded lubricants become very resistant to foaming, even under drastic service conditions.

In making up compounded lubricants-of this type it is advantageous to dissolve the aminophosphate in the oil first, as thereby foaming is prevented during the step of mixing in the extreme pressure agent or other additive. But so far as performance of the lubricant in service is concerned, the order of addition makes no difference.

The following example illustrates the properties of an extreme pressure gear lubricant prepared in accordance with the invention.

Example IIL-A modern gear lubricant contains 92.0 per cent by volume of a highly refined viscous Pennsylvania oil and 8.0 per cent, of a special synthetic mixture containing around 10 per cent sulfur. A similar lubricant prepared accordingto the invention contains these oils in the proportions of 92.0 per cent and 8.0 per cent, respectively, and 0.04 per cent of 2,6-lutidine isoamyl octyl phosphate. The viscosity of the modern gear lubricant was 1918 SUV. at 100 F., 767 at 130 F., and 141 at 210 F. The viscosity of the improved lubricant was only negligibly different from this, and the same was true of the other characteristics-gravity, viscosity index, flash and fire tests, pour test, color, sulfur, copper strip tests, centrifuge test .(for gravity-separable matter), and carbon residue. The neutralization number of the new lubricant was 0.56 against 0.50 for the old. The surface tensions were nearly identical. The Almen and Timken tests, indicative of the lubricating value To evaluate the foaming tendency of petroleum oils compositions, a test-was devised which affords an exceptionally accurate indication of the comparative foaming tendencies. A sample of oil is subjected to very drastic foaming conditions under a standardized procedure which makes it pos sible to determine quantitatively the tendency of the oil to foam and the stability or permanency of the foam produced. In general it resembles a somewhat similar testing method employed by the General Motors Corporation for determining the foaming tendencies of gearin lubricants, but has been modified in the direction of greater accuracy and in order to make it possible to record more comprehensive test data.

Foaming test (No. 1)

An agitating means is provided which is an adaptation of an ordinary commercial motordriven household mixer-a' "Sunbeam Mixmaster," Model 1, manufactured by the Flexible Shaft Company, Chicago, Ill. The device employed in the test is the usual household model with two slight changes; the turntable of the usual house hold mixer is replaced by a rigid platform, and a cylindrical brass container having an inside diameter of 7 inches and an inside height of 4 inches is substituted for the usual household glass mixing bowl. The container is fitted with a gage for measuring the depth of oil or oil and foam therein before and after agitation.

The agitator device itself comprises a. pair of motor-driven beaters which are of the convex outside surface type as described in U. 8. Patent 2,161,881, each beater having a pair of blades of the type indicated and being so positioned with respect to each other that the two pairs of beater elements are at right angles and rotate in opposite directions in closely spaced, overlapping paths. In operating position, the heaters are perpendicular to the base of the mixer, as shown in Patent 2,161,881. In the present test, they are centered in the container, and the bottom of the beaters is spaced approximately 1; inch from the controlled within.; R. r. M.v

minutes.

employed if a still more drastic-testis required.)

.The beatersarerotated ata speed of 5 50 B. P. M.

A measured sample of. 500 cc. (cc) of oil is introduced into the containenthe temperature of the sample is brought to 77 F., and the container is then placed in position and the beater elements lowered into operating position.

The motor is-startedand adjusted to the speed indicated above.- Thebeaters agitate theoil and a ar-s8 l w n mp 9m tur i treatedaccording' to the invention behaves under such-Ponditions.

Example IV.- -A turbine. oil was subjected .to," test,No. 3. After 15 minutes agitation, the oil plus foam meas- .ured 800 .cc.,. as. compared with' too it. for the original oil. The sameoilaiter'treating with 0.01 per cent 2,6-lutidine isoamyl' octyl phosbeat air intothe sample. .Asitation is continued 1.10 phate showed'only 540 cc. of oil-plus'foam.

for exactly 15 minutes.

'The motor is now stoppedthe beatersare rei moved from the oil, and any oil'or foam adherin to the heaters is permitted'to drain into the container, which takesone' or two minutes. The foam level -'is then immediately determined, and

the temperature of the, sample ismeasured'j. his

' as, for example,v by changing the size of the sample, the speed of agitation or the time of asita; tion, or by taking the final measurements ,at an earlier or later period. However, in the test-re ferred to in the specific example above, the'pro cedure was precisely as indicated.

Test No. 21s the same as test No. 1 except that agitation is continued for 44 hours instead of 15 (Longer periods of agitation may be In some very low viscosity oils, considerable foam may develop during agitation, which disappears very quickly when agitationis stopped. These conditions are found, for-example, :in

-proved lubricants similar to those illustrated'in In the practice of our invention, other lutidines may be used in lieu of 2,6-lutidine informing our.

new agents and such otherlutidine phosphate compounds are likewise excellent foam suppressors, and maybe employediinmaking im- Example 11,111, and IV ante. That is, whlle our inventidrrhas been'des'cribed above with refermarine turbine lubrication; systems (which use light oils) at the point .,where returned on is discharged violently into a 'rservoir. ',To evaluate foaming in such' cases, thereisemployedaaithird test, No. 3, similar in allrespects tmtest N03 'ence to va'rious'speciflc examples and embodiments, it willbe understood that the'invention is not" limited to suchillustrative examples and embodiments, but'may be variously practiced within the scope oithe claims herein made.

1; A mineral oilcomposition resistant to foaming, comprising mineral oil and a small proportion of a lutidine isoamyl octyl phosphate.

2. The composition of claim 1 wherein the'proportion of said lutidine phosphate salt is between 9.91 and .1.0 per cent by weight of thje composition.

3. The composition of claim 1 wherein the said lutidine phosphatesalt is 2, 6-dimethyl pyridine isoamy l octyl phosphate.

4. A mineral oil resistant pct of lutidine and isoamyl octyl orthophosphate', said reaction product being an oil soluble liquid.

',5;.' Agar lubricant comprising aviscous min- 'eral i lubricating. oil, an extreme pressure agent pi a characteristic such as to increase tendency jof theoil to foam, and 'a'smauprb ornon; Sum

.45 c'ient' tof' prevent" foaminglof lutidine isoamy' qtv bh sph ta smn'm.

TROY 'IL"'CAN'I.'REIL.

highly refined TPennsylvania 'to ioaniing, com-1 prising a small proportion'oi' the reaction prod- 

